The present invention relates to a personal communications apparatus, for example a cellular telephone handset, having an antenna diversity arrangement.
In cellular telecommunications systems radio signals are transmitted from a base station to a mobile station and vice versa. The radio signals transmitted by cellular base stations are normally vertically polarised. Cellular handsets typically have an antenna, such as a normal mode helix or extendible monopole, mounted at the top of the handset and approximately in line with the longest axis (median plane) of the handset. Such antennas are therefore polarised along this axis, so that when the handset is held vertically the antenna is vertically polarised.
However, cellular handsets are typically held at an angle of between 45xc2x0 and 75xc2x0 to the vertical direction, with a mean of about 60xc2x0, to align the microphone with the user""s mouth and the loudspeaker with the user""s ear (Mobile Antenna Systems Handbook, K Fujimoto and J R James, Artech House, 1994, page 227). By holding the handset at such an angle a polarisation loss is introduced in the transmission of signals between the handset and base station.
This problem has been recognised, for example in EP-A-0 652 646 which discloses a cellular handset having a pivoted antenna mast which is weighted so that the mast remains substantially vertical for a wide range of handset orientations. However, such an arrangement requires significant space inside the handset and is prone to jamming.
Additional problems with the use of cellular handsets are multipath fading, caused by signals from the base station to the handset travelling along paths of different lengths, and various other types of interference. Such problems can be addressed by the use of antenna diversity or other spatial processing techniques.
An object of the present invention is to provide a personal communications apparatus having improved radio reception.
According to the present invention there is provided a personal communications apparatus comprising a body including transceiver circuitry and an antenna diversity arrangement comprising first and second antennas arranged having their respective polarisation axes oppositely inclined to the median plane of the body.
Although the inclination of the antennas would normally be symmetrical about the median plane, this will not always be the optimum orientation. For example, if a plane through the location of the handset""s microphone and loudspeaker is not parallel to the median plane the antennas may be inclined symmetrically with respect to this plane instead (since it is location of the microphone and loudspeaker that determines the orientation of the handset in normal use). Hence, in the present specification and claims the term xe2x80x9cmedian planexe2x80x9d is to be understood to include a plane through the microphone and loudspeaker, especially when these are not arranged on the plane of symmetry of the body.